The present invention relates to a method for fabricating electric interconnections to be used for electronic circuit boards of electric equipment such as a flat panel display or a two-dimensional image detector, further relates to an interconnection substrate applicable to a variety of electronic devices, relates to display devices such as a liquid crystal display (LCD), a plasma display (PDP), an electrochromic display (ECD), an electroluminescent display (ELD) and relates to an image detector using light or radial rays.
Conventionally, in a flat panel display represented by the liquid crystal display, display material such as liquid crystal or electric discharge gas is normally held between a pair of substrates, and a voltage is applied to this display material. In this stage, electric interconnections made of conductive material are provided at least on one substrate.
For example, in the case of an active matrix drive type display, gate electrodes and data electrodes are arranged in a matrix form on one substrate (active matrix substrate) of a pair of substrates that hold the display material between them, and a thin film transistor (TFT) and a pixel electrode are arranged at each intersection. These gate electrodes and data electrodes are normally made of a metal material such as Ta, Al or Mo and formed into a film by a dry film forming method such as a sputtering method.
There has also been developed a flat panel type two-dimensional image detector obtained by combining an active matrix substrate having a construction similar to that of the aforementioned active matrix drive type display with a photodetector element or an X-ray detecting element. The details of the two-dimensional image detector are disclosed in the reference documents of xe2x80x9cL. S Jeromin, et al., xe2x80x9cApplication of a-Si Active-Matrix Technology in X-Ray Detector Panelxe2x80x9d, SID 97 DIGEST, p.91-94, 1997xe2x80x9d, xe2x80x9cJapanese Patent Laid-Open Publication No. HEI 6-342098xe2x80x9d and others.
If it is tried to increase the area and improve the definition of the flat panel display or the two-dimensional image detector of the above kind, then the resistance and parasitic capacitance of the electric interconnections increase as the drive frequency increases, and accordingly, the delay of the drive signal emerges as a serious problem.
Therefore, in order to solve the problem of this drive signal delay, it is tried to use low electric resistance Cu (bulk resistivity is 1.7 xcexcxcexa9xc2x7cm) as an interconnection material instead of the conventional interconnection materials of Al (bulk resistivity is 2.7 xcexcxcexa9xc2x7cm), xcex1-Ta (bulk resistivity is 13.1 xcexcxcexa9xc2x7cm) and Mo (bulk resistivity is 5.8 xcexcxcexa9xc2x7cm). There is a disclosure of the examination of a TFT liquid crystal display (TFT-LCD) employing Cu as a gate electrode material in, for example, the reference of xe2x80x9cLow Resistance Copper Address Line for TFT-LCDxe2x80x9d (Japan Display ""89 p.498-501). This reference document states clearly the necessity for improving the adhesion by interposing a metal film of Ta or the like on the groundwork since the Cu film formed by the sputtering method has poor adhesion to the groundwork glass substrate.
However, in the case of the interconnection structure in which a metal film of Ta or the like is provided as an interposition on the above-mentioned groundwork, the Cu film and the groundwork metal film of Ta or the like need individual dry film forming processes and etching processes, and this disadvantageously causes an increased number of processes and cost increase.
In view of the above, the prior art reference of Japanese Patent Laid-Open Publication No. HEI 4-232922 proposes electric interconnection fabricating method for using a transparent electrode made of indium-tin-oxide (ITO: tin-added indium oxide) or the like as a groundwork film and forming by a technique of plating the surface of the groundwork film with a metal film of Cu or the like. According to this technique, there is clearly stated the effect of allowing Cu interconnections to be efficiently formed even in a large area since the plating metal can be formed as a film selectively on the ITO film and therefore the patterning process is necessary for only the ITO film of the transparent electrode. There is also stated a structure for interposing a metal film of Ni or the like having a good adhesion property between ITO and Cu.
There has also been proposed electric interconnection fabricating method for forming a metal film of Ni, Au, Cu or the like on a patterned ITO film by a plating technique for the various purposes of reducing the processes of the active matrix substrate, reducing the resistance of the transparent electrode of a simple matrix type liquid crystal display device, increasing the solder wettability on the ITO film and so on besides the electric interconnection fabricating method described in the aforementioned prior art reference of Japanese Patent Laid-Open Publication No. HEI 4-232922 (refer to, for example, the prior art reference documents of Japanese Patent Laid-Open Publication No. HEI 2-83533, Japanese Patent Laid-Open Publication No. HEI 2-223924, Japanese Patent Laid-Open Publication No. SHO 62-288883 and Japanese Patent Laid-Open Publication No. HEI 1-96383).
However, in the case of the electric interconnection fabricating method using ITO for the groundwork, the metal film is formed by the plating technique using no vacuum film forming apparatus. However, the ITO film that becomes the groundwork of the metal film is formed still by a vacuum film forming apparatus of the sputtering method or the vacuum deposition method. This leads to the problem that a sufficient cost reduction effect cannot be obtained and the method cannot easily cope with a large-area substrate.
Accordingly, an object of the present invention is to provide an electric interconnection fabricating method, an interconnection substrate, a display device and an image detector, which is able to be fabricated at low cost and to easily cope with a large-area substrate using no vacuum film forming apparatus.
In order to achieve the aforementioned object, the present invention provides an electric interconnection fabricating method comprising: an oxide film forming process for forming an oxide film on an insulating substrate by a first wet type film forming technique; and a metal film forming process for forming a metal film on the oxide film by a second wet type film forming technique.
According to the above invention, the electric interconnections having the laminate structure formed of the metal film and the oxide film can be obtained using no vacuum film forming apparatus, and the sufficient cost reduction effect can be obtained by comparison with the conventional electric interconnection fabricating method. The first and second wet type film forming techniques can easily cope with the large-area substrate since the first and second wet type film forming techniques can more easily form a large-area film than the vacuum film forming technique. The electric interconnections having a laminate structure formed of the metal film and the oxide film can be obtained without using any vacuum film forming apparatus. Therefore, electric interconnections can be easily formed on an insulating substrate (a polymer film, for example) or the like made of an organic material besides a glass substrate having excellent vacuum resistance and heat resistance. Furthermore, electric interconnections can be formed with high productivity according to a roll-to-roll system using a long film base material.
In one embodiment of the present invention, the electric interconnection fabricating method further comprises a patterning process for patterning the oxide film according to a specified shape between the oxide film forming process and the metal film forming process.
According to the above embodiment, the metal film formed through the metal film forming process can be selectively formed only on the oxide film patterned according to a specified shape through the patterning process. Therefore, the metal film is formed only in the required portion by comparison with the case where an oxide film and a metal film are formed on the entire surface of an insulating substrate and thereafter both the films are patterned. Accordingly, the patterning of the metal film becomes unnecessary, and also no waste of the metal film material is generated.
In one embodiment of the present invention, a precursor of the oxide film has photosensitivity and the patterning process for patterning the oxide film according to the specified shape comprises a process for applying light to the precursor of the oxide film.
According to the above embodiment, neither resist coating process nor resist removing process is required between the oxide film formation and the patterning process, and therefore, the producibility can be improved.
In one embodiment of the present invention, the first wet type film forming technique used for the oxide film forming process is a sol-gel method.
The above-mentioned sol-gel method is a sort of wet type film forming technique and includes the processes of using a metal organic compound or an inorganic compound as a solution, promoting the hydrolysis and polycondensation of a compound in the solution so as to fix a sol as a gel and forming an oxide solid through the heating of the gel. According to the above embodiment, the oxide film can be easily formed by merely coating a sol-gel solution on the insulating substrate of glass or the like and sintering the same by the sol-gel method using no vacuum film forming apparatus. Furthermore, according to the sol-gel method, there can be formed a multi-porous oxide film in which minute holes exist in a network style as compared with the smooth surface of the oxide film formed by the vacuum film forming apparatus. Therefore, if the oxide film obtained by the sol-gel method is plated with a metal film, then the minute holes of the oxide film produce an anchor effect, allowing a plating film of a very good adhesion property to be obtained. This also allows electroless Cu plating to be effected on an ITO film, which has conventionally been difficult.
In one embodiment of the present invention, the first wet type film forming technique used for the oxide film forming process is either a chemical deposition method or a liquid phase deposition method.
The chemical deposition method is the method of immersing an insulating substrate in an aqueous solution and depositing an oxide film on the insulating substrate through a redox reaction in the aqueous solution. The liquid phase deposition method (LPD method) is the method of depositing an oxide film on an insulating substrate through a hydrolytic equilibrium reaction of a metallic fluoro-complex or hydrosilicofluoric acid. According to the embodiment, an oxide film can be easily formed by merely immersing an insulating substrate in an aqueous solution by the chemical deposition method or the liquid phase deposition method using no vacuum film forming apparatus. According to the oxide film obtained by the chemical deposition method, crystal grains grow around a core of a metal catalyst made to adhere to the surface of the insulating substrate. Therefore, the surface becomes more undulated than that of the oxide film formed by the vacuum film forming apparatus. Therefore, if the oxide film obtained by the chemical deposition method is plated with a metal film, then the surface unevenness of the oxide film produces an anchor effect, allowing a plating film of a very good adhesion property to be obtained.
In one embodiment of the present invention, the second wet type film forming technique used for the metal film forming process is a wet type plating method.
According to the above embodiment, in the case of the electroplating of the wet type plating technique that is classified roughly into electroplating and electroless plating, a metal film is deposited on the surface of the cathode by arranging a metal that serves as an anode and the cathode (electrode subjected to plating) in a plating liquid in which metal ions are dissolved and flowing a direct current through the plating liquid. Therefore, if the oxide film of the groundwork formed through the oxide film forming process has conductivity, then it is allowed to deposit a metal film on only the oxide film by making the oxide film serve as a cathode. In the case of the electroless plating (reduction plating or displacement plating), a metal film can be deposited flowing no current through the plating liquid. Therefore, a metal film can be deposited regardless of the presence or absence of the conductivity of the oxide film of the groundwork formed through the oxide film forming process. A plating film having a great film thickness can be formed even in a large area since a current distribution density influences less than in the case of electroplating. Furthermore, by performing the process for making the catalyst adhere selectively to only the surface of the oxide film in this stage, a metal film can also be deposited selectively on only the oxide film. Thus, by using the wet type plating method for the wet type film forming technique of the metal film forming process, a metal film can be easily formed using no vacuum film forming apparatus.
In one embodiment of the present invention, the oxide film has a plating catalyst.
According to the above embodiment, the process of providing the plating catalyst can be eliminated when forming a metal film on the oxide film by electroless plating in a subsequent process.
In one embodiment of the present invention, the oxide film is a conductive oxide film.
According to the above embodiment, a metal film can be formed on the conductive oxide film by electroplating by providing the oxide film by a conductive oxide film.
In one embodiment of the present invention, the conductive oxide film has transparency.
According to the above embodiment, by providing the oxide film by a conductive oxide film having transparency, the transparent electrode provided for each pixel of, for example, a liquid crystal display device or a two-dimensional image detector besides the electric interconnections can be formed of the same transparent conductive oxide film, allowing the reduction in number of processes to be achieved.
In one embodiment of the present invention, the conductive oxide film is a film to be used for the electric interconnections and an application other than the electric interconnections and is formed of an identical material on the insulating substrate through an identical process.
According to the above embodiment, if it is required to form a film of a transparent conductive film (for example, a transparent electrode provided for each pixel) other than the use of electric interconnections as in the liquid crystal display device or a two-dimensional image detector, then a transparent conductive oxide film formed of an identical material through an identical process can be used for the electric interconnections and as a film for the use other than the electric interconnection use. This allows the reduction in number of processes and efficient fabrication of electric interconnections.
In one embodiment of the present invention, the metal film is either a single layer film made of any one of nickel (Ni), copper (Cu) and gold (Au) or a multi-layer film including at least one layer of a single layer film made of any one of nickel (Ni), copper (Cu) and gold (Au).
According to the above embodiment, the Ni film can be formed on the oxide film (ITO film etc.) with a good adhesion property, and electroless plating can be performed selectively on only the oxide film (ITO film etc.). Further, Cu and Au have a low specific resistance, and this can achieve electric interconnections having a low resistance. In particular, by forming an Ni film on the oxide film (ITO film) and further forming a Cu, Au or Cu/Au film on the Ni film, then electric interconnections having a low resistance and a good adhesion property can be provided.
In one embodiment of the present invention, an interconnection substrate comprises electric interconnections of a laminate structure including an oxide film formed on an insulating substrate by a first wet type film forming technique and a metal film formed on the oxide film by a second wet type film forming technique.
According to the interconnection substrate of one inventive aspect, electric interconnections having a laminate structure formed of a metal film and an oxide film can be obtained without using any vacuum film forming apparatus, allowing a sufficient cost reduction effect to be obtained as compared with the case where electric interconnections formed by the conventional fabricating method is used. The first and second wet type film forming techniques can easily cope with a large-area substrate since the film formation in a large area can be easily achieved by comparison with the vacuum film forming technique. Furthermore, electric interconnections having the laminate structure formed of the metal film and the oxide film can be obtained without using any vacuum film forming apparatus. Therefore, electric interconnections can be easily formed on an insulating substrate (for example, a polymer film) or the like made of an organic material besides the glass substrate having excellent vacuum resistance and heat resistance. Furthermore, electric interconnections can be formed with good productivity according to a roll-to-roll system using a very long film material taking advantage of the merit that no vacuum system is used.
In one embodiment of the present invention, the oxide film is patterned according to a shape of interconnections and the metal film is formed selectively on the patterned oxide film.
According to the above embodiment, the metal film is formed only in the necessary portion by comparison with the case where the oxide film and the metal film are both formed on the entire surface of the insulating substrate and thereafter patterned according to the shape of interconnections. Therefore, the metal film patterning process becomes unnecessary, and also no waste of the metal film material is generated.
In one embodiment of the present invention, the precursor of the oxide film has photosensitivity.
According to the above embodiment, the oxide film can be patterned according to the specified shape by applying light to the precursor of the oxide film, and neither resist coating process nor resist removing process is needed between oxide film formation and the patterning, and therefore, the producibility can be improved.
In one embodiment of the present invention, the oxide film is a multi-porous film.
According to the above embodiment, if the surface of the multi-porous oxide film is plated with a metal film, then the minute holes of the oxide film produce an anchor effect, allowing a plating film of a very good adhesion property to be obtained. This allows electroless Cu plating to be effected on an ITO film, which has conventionally been difficult.
In one embodiment of the present invention, the oxide film is a film having surface unevenness.
According to the above embodiment, the surface unevenness of the oxide film produces an anchor effect, allowing a plating film of a very good adhesion property to be formed on the oxide film.
In one embodiment of the present invention, the oxide film is a conductive oxide film.
According to the above embodiment, a metal film can be formed on the conductive oxide film by electroplating by providing the oxide film by the conductive oxide film.
In one embodiment of the present invention, the conductive oxide film has transparency.
According to the above embodiment, by providing the oxide film by a conductive oxide film having transparency, the transparent electrode provided for each pixel of, for example, a liquid crystal display device or a two-dimensional image detector besides the electric interconnections can be formed of the same transparent conductive oxide film, allowing the reduction in number of processes to be achieved.
In one embodiment of the present invention, the metal film is either a single layer film made of any one of nickel (Ni), copper (Cu) and gold (Au) or a multi-layer film including at least one layer of a single layer film made of any one of nickel (Ni), copper (Cu) and gold (Au).
According to the above embodiment, the Ni film can be formed on the oxide film (ITO film etc.) with a good adhesion property, and electroless plating can be performed selectively on only the oxide film (ITO film etc.). Further, Cu and Au have a low specific resistance, and this can achieve electric interconnections having a low resistance. In particular, by forming an Ni film on the oxide film (ITO film) and further forming a Cu, Au or Cu/Au film on the Ni film, then electric interconnections having a low resistance and a good adhesion property can be provided.
In one embodiment of the present invention, a display device comprises the above interconnection substrates.
According to the above embodiment, a display device that can be fabricated at low cost without using a vacuum film forming apparatus and is able to cope with a large-area substrate can be provided.
In one embodiment of the present invention, an image detector comprises the above interconnection substrates.
According to the above embodiment, an image detector that can be fabricated at low cost without using a vacuum film forming apparatus and is able to cope with a large-area substrate can be provided.